60 research outputs found
Diffractive Higgs production
Instrumenting the LHC to measure the outgoing protons in the process pp ->
p+X+p opens up new possibilities for physics studies in the Standard Model and
beyond. In this talk I first present an overview of the underlying QCD
calculation and its uncertainties. I then move on to present a variety of new
physics scenarios which one would want to explore via this unique channel.
There is a short discussion of the recent CDF data which may provide evidence
for the existence of central exclusive jet production at the Tevatron.Comment: 8 pages. Talk presented at "Diffraction 2006
High-t Diffraction
The study of those rapidity gap processes where a large momentum is transferred across the rapidity gap provides an ideal opportunity to understand the gap producing mechanism wholly within the framework of QCD perturbation theory. The current theoretical and experimental status of this `high-t diffraction' is reviewed.The study of those rapidity gap processes where a large momentum is transferred across the rapidity gap provides an ideal opportunity to understand the gap producing mechanism wholly within the framework of QCD perturbation theory. The current theoretical and experimental status of this `high-t diffraction' is reviewed
Parton branching at amplitude level
We present an algorithm that evolves hard processes at the amplitude level by
dressing them iteratively with (massless) quarks and gluons. The algorithm
interleaves collinear emissions with soft emissions and includes
Coulomb/Glauber exchanges. It includes all orders in , is spin
dependent and is able to accommodate kinematic recoils. Although it is
specified at leading logarithmic accuracy, the framework should be sufficient
to go beyond. Coulomb exchanges make the factorisation of collinear and soft
emissions highly non-trivial. In the absence of Coulomb exchanges, we show how
factorisation works out and how a partial factorisation is manifest in the
presence of Coulomb exchanges. Finally, we illustrate the use of the algorithm
by deriving DGLAP evolution and computing the resummed thrust, hemisphere jet
mass and gaps-between-jets distributions in .Comment: 54 pages, minor changes in version
Diffraction 2006: Theoretical Summary
This paper presents a summary of the theoretical presentations to the
international workshop "Diffraction 2006". The range of topics covered during
the workshop was quite broad and this summary is therefore somewhat selective
covering recent developments in BFKL physics, exclusive processes, saturation
dynamics, DIS and structure functions and coherence in QCD.Comment: 16 pages. Talk presented at "Diffraction 2006
Precise Predictions for Higgs Production in Neutralino Decays in the Complex MSSM
Complete one-loop results are obtained for the class of processes
chi^0_i->chi^0_j h_a in the MSSM where all parameters entering this process
beyond lowest order are allowed to have arbitrary CP-violating phases. An
on-shell renormalisation scheme is worked out for the chargino-neutralino
sector that properly takes account of imaginary parts arising from complex
parameters and from absorptive parts of loop integrals. The genuine vertex
contributions to the neutralino decay amplitudes are combined with two-loop
propagator-type corrections for the outgoing Higgs boson. In this way the
currently most precise prediction for this class of processes is obtained. The
numerical impact of the genuine vertex corrections is studied for several
examples of CP-conserving and CP-violating scenarios. We find that significant
effects on the decay widths and branching ratios are possible even in the
CP-conserving MSSM. In the CP-violating CPX benchmark scenario the corrections
to the decay width are found to be particularly large, namely, of order 45% for
a Higgs mass of 40 GeV. This parameter region of the CPX scenario where a very
light Higgs boson is unexcluded by present data is analysed in detail. We find
that in this parameter region, which will be difficult to cover by standard
Higgs search channels at the LHC, the branching ratio for the decay
chi^0_2->chi^0_1 h_1 is large. This may offer good prospects to detect such a
light Higgs boson in cascade decays of supersymmetric particles.Comment: 24 pages, 6 figure
Coulomb gluons and the ordering variable
We study in detail the exchange of a Coulomb (Glauber) gluon in the first few
orders of QCD perturbation theory in order to shed light on their accounting to
all orders. We find an elegant cancellation of graphs that imposes a precise
ordering on the transverse momentum of the exchanged Coulomb gluon.Comment: 28 pages, 12 figure
Ordering multiple soft gluon emissions
We present an expression for the QCD amplitude for a general hard scattering
process with any number of soft gluon emissions, to one-loop accuracy. The
amplitude is written in two different but equivalent ways: as a product of
operators ordered in dipole transverse momentum and as a product of
loop-expanded currents. We hope that these results will help in the development
of an all-orders algorithm for multiple emissions that includes the full colour
structure and both the real and imaginary contributions to the amplitude.Comment: v4: 3 pages; 1 figure, 4 references and small clarifications added.
Version accepted for publication in Physical Review Letter
Diffractive production of high photons at a future linear collider
We examine the prospects for studying the diffractive production of high pt photons in the process gamma+gamma -> gamma+X at a future linear collider operating in both ee and gamma-gamma modes. The high luminosity associated with a linear collider make it the ideal place to measure this process
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